It is previously known to build offshore power stations at the extraction sites of the deposits and to consume the extracted natural gas directly at the extraction site instead of transporting the gas ashore over pipe lines. For this purpose semi-submerged floating platforms are used, and these platforms are held at a constant level over the bottom of the sea by means of a number of vertical wires attached directly to the bottom or to a number of separate anchors. However, it is difficult and time consuming to anchor and stabilize these platforms in such a way that the work necessary for connecting the platforms to cables and pipes can be done rapidly and with the smallest possible risk for the workers who have to carry out the work operations. These work operations include complicated operations to be carried out by divers for the connection and coupling of tubes, pipes and cables at the platforms and at the bottom of the sea. If the divers have to go down into the water from diving ships or platforms, particularly at high sea, they run the risk of hurting themselves on the sides of the ships or platforms. Furthermore, if the platforms are not firmly anchored in relation to the bottom of the sea, it is difficult and dangerous to connect gas conduits or pipes from the bottom of the sea and electric cables with the couplings or connections on the platforms.